Field of the Invention
This invention relates to the field of leak detection by acoustical means in storage tanks.
Description of the Related Art
One of the most common ways of storing hydrocarbons, such as crude oil, gasoline and the like is in large metal storage tanks which are normally cylindrical in shape with the bottom resting on a base of soil or other material. Many precautions are made to improve the engineering of these tanks to prevent them from leaking. However, despite all of this effort these tank do develop leaks. These leaks are harmful in at least two ways: (1) They can cause pollution of the underground soil and possibly underground water sources; and (2) the loss of the material itself is loss of a natural resource and this can also be costly in terms of dollars. For example, if one tank leaks more that two barrels of fluid per day the loss would be more than 30,000 gallons per year. These tanks may be 100 to 200 feet in diameter and may contain upward to 100,000 or more barrels of fluid. If there are 25 such tanks in a tank farm then there could be a leakage of as much as 750,000 to 2,000,000 gallons of fluid per year.
Acoustical detection of leaks in the bottom of storage tanks usually consists of placing multiple sensors around and in the tank and connecting such sensors to amplifying, analyzing and display means. Since the passage of fluid through a leak creates vibrations, this is an "acoustical event" that may be detected and localized.
Acoustical leak detectors usually require that a leak be "active" to be detectable (i.e. the leak must be passing material to create turbulence which is acoustically detected). Leaks which are equilibrated with no passage of materials are not detectable by present acoustical methods; likewise leaks with a very low flow rate are difficult to detect. Prior attempts to overcome these limitations have included: (1) varying the liquid storage levels in tanks to force fluid out of the leaks to generate a detectable sound; (2) requiring absolute silence in and around the tank; (3) using prolonged testing times, often over an hour. Generally, small leaks (less than 1/8th inch) are not detectable by prior art means.